Fatigue lifetime study of piezoceramic patch transducers
This study investigates the loading limits and fatigue behavior of laminar piezoceramic patch transducers, based on monolithic lead zirconate titanate (PZT) plates encapsulated in epoxy resin matrix. Testing includes tensile and compressive mechanical loading, at different temperatures, as well as electric actuation. The objective is the identification of typical failure mechanisms and suitable models for failure and lifetime analysis. In tensile loading, which is observed to have the strongest influence on the patch lifetime, the relevant failure mechanism in quasi-static and cyclic loading is found to be cracking of the PZT plate, causing degradation of the patch performance. Based on the micro-structural investigations and FE simulation, the fracture toughness of the PZT plate is analyzed and a micro-crack-propagation-based fatigue lifetime model is derived. The effect of the fragmentation of the piezoceramic plate on the patch performance is analyzed by the presented functional length concept, based on the shear lag model, yielding very good quantitative agreement.